1. Field of the Invention
The present invention pertains to an apparatus and method of stimulating the vestibular system of a patient to provide a therapeutic benefit, and, in particular, to an apparatus and method in which the portions of the labyrinth associated with the labyrinthine sense and/or the nerves associated therewith are stimulated to perform at least one of the following functions: augment or control a patient's respiratory function, open the patient's airway, induce or promote sleep, counteract vertigo, or a combination of these functions.
2. Description of the Related Art
There are numerous techniques for providing respiratory assistance to a patient suffering from a respiratory disorder and/or dysfunction. For example, it is known to provide mechanical ventilatory assistance by delivering a flow of breathing gas to the patient's airway via a ventilator. This mechanical ventilation method of assisting the patient's respiratory effort has numerous disadvantages that are well documented. For example, the patient interface device, such as a tracheal tube, intubation tube and nasal/oral mask, can be difficult to place within or on the patient, may cause long-term problems in the patient, and/or may not be tolerated by the patient. In addition, because the mechanical ventilator replaces, either partially or completely, the respiratory effort of the patient, the patient may have difficulty being weaned off of the ventilator, especially if the patient has been using a ventilator for an extended period of time.
It is also known to provide ventilatory assistance to a patient by directly stimulating the patient's phrenic nerve, thereby causing the diaphragm to contract. It is also known to provide this so called "electroventilation" technique by placing electrodes on the chest of the patient to innervate the diaphragm or chest muscles directly. See, e.g., U.S. Pat. No. 4,827,935 to Geddes et al. entitled, "Demand Electroventilator." However, these conventional electroventilation techniques are relatively ineffective at imitating the natural respiratory function of the patient, because, in a normal patient, each respiratory effort involves a complex interaction of nerve and muscle stimulation that includes more tissues than just the phrenic nerve and diaphragm. Conventional electroventilation techniques target individual muscles or, at best, muscle groups, not the overall neural-muscular systems that cooperate to produce a normal respiratory cycle.
There are also numerous techniques for maintaining airway patency and/or patient ventilation to treat sleep apnea syndrome. For example, a common technique for treating obstructive sleep apnea (OSA) is to provide the patient with a continuous positive airway pressure (CPAP) or a bi-level pressure that varies depending on whether the patient is in the inspiratory or expiratory phase of the respiratory cycle. The supply of gas to the patient provides a pneumatic splint for the portion of the airway that would otherwise collapse. It is also known to treat central sleep apnea (CSA) using a system similar to a non-invasive ventilator. Preferably, the CSA treatment system detects whether the patient has stopped breathing for a period of time that exceeds a predetermined threshold time period and provides ventilatory assistance if this occurs. These techniques for treating sleep apnea syndrome have disadvantages similar to those associated with providing ventilatory assistance to the patient; namely, some patients have difficulty tolerating the patient interface device. In addition, some patients have difficulty and/or are uncomfortable breathing against the flow of gas being delivered to their airway. Also, because these systems are used while the patient sleeps, they must be kept as quite as possible so as not to arouse the user or the user's sleep partner.
It is also known to treat OSA by electrically stimulating the musculature in the neck area associated with the upper airway. Relaxation of these muscles during sleep is believed to be a contributing, if not a primary, factor on the occurrence of OSA for many sufferers. One conventional method of electrically stimulating the muscles in the upper airway involves placing an electrode in direct contact with a surface of the patient and passing a current through the surface tissues to stimulate the underlying muscles. For example, an intraoral appliance has been developed that applies an electrical current within the oral cavity to induce contraction of the genioglossus muscle, thereby helping to maintain airway patency. Another known electrical stimulation appliance applies electrical energy to the exterior surface of the patient's neck below the chin to induce contraction of the underlying upper airway muscles.
Electromuscular stimulation using surface mounted electrodes creates relatively large current densities at the site of the electrodes. Because these current densities are disposed at the surface of the patient, which also typically contains a relatively large number of nerve endings, such electrical stimulation devices might, in some cases, cause unpleasant sensations, possibly arousing the user from sleep. In addition, some patients may not be comfortable wearing an electrical stimulation appliance either on their neck or in their mouth while they sleep.
It is also known to apply electrical stimulation directly to the nerves and/or muscles of the upper airway via electrodes implanted in the patient to induce tension in the muscles of the upper airway, thereby preventing them from collapsing during sleep. As with stimulating the phrenic nerve to induce respiration, these conventional neuralmuscular electrical stimulation techniques are relatively ineffective at imitating the natural upper airway muscle contraction function that takes place during normal breathing. Normal breathing involves a complex interaction of nerve and/or muscle stimulation that is precisely timed and is provided at precise stimulation levels so as to prevent airway collapse. Direct invasive, stimulation of the nerves and/or muscles associated with the upper airway targets one nerve/muscle specifically, and, therefore, does not reproduce the overall neuromuscular function of a normal human that is involved in maintaining airway patency during normal breathing. In addition, direct invasive stimulation of the nerves and/or muscles associated with the upper airway is considered to be relatively invasive medical procedure, and, therefore, may not be favored by a large number of patient's and/or caregivers.
It is also known to treat sleep apnea syndrome through surgical removal of tissues in the upper airway. In addition, pharmacological solutions have also been pursued, at least with respect to the treatment of central sleep apnea. However, neither of these therapies is successful in all cases. Surgical removal of tissue is invasive, introduces a potential for complications, the long term effects are not known, and is only marginally successful. Pharmacological therapy has been, in general, less than satisfactory, and side effects are frequent.
There are many patients that suffer from sleeping disorders in addition to or other than sleep apnea syndrome. For example, many people have difficulty falling asleep. Although the specific pathological reasons why some people have difficulty falling asleep are not believed to be known, many phramacological solutions exist for assisting a person to fall asleep. However, such medications, which are essentially relaxants, may not be appropriate for some people, due to undesirable, known, or unknown drug interactions, for example, and, therefore, are disfavored by some patients and/or caregivers. In addition, these medications may produce undesirable side effects, such as excessive drowsiness. More seriously, these medications may be contraindicated, and, therefore, a health risk.
It is also known that physically rocking the patient can be helpful in inducing sleep. To this end, beds with mechanical rocking mechanisms have been developed. It can be appreciated, however, that the rocking motion may not be tolerated by the patient's bed partner. In addition, providing a bed that can rock an adult requires relatively costly, mechanically complicated, and potentially noisy rocking mechanisms to move the bed in the desired rocking direction. In addition, such rocking beds are typically cumbersome, aesthetically displeasing and not practical in many homes.
Although not related to respiration or sleep, another disjunction of interest with respect to the present invention is vertigo and/or dizziness, which are disorders in which the sufferer has the sensation that they or their surroundings are whirling. These disorders may be induced by pathological reasons or from the physical movement of the user, such as spinning in a disorienting fashion. Vertigo, for example, may also be the result of an inner ear disorder that effects the patient's balance system. Depending on the underlying cause, treatment of these disorders include physical therapy, cranial manipulation, surgery, and pharmacological intervention. However, some causes of vertigo and/or dizziness have no cure or treatment. Furthermore, the existing physical therapies, cranial manipulation treatments, and surgeries are time consuming, may be only moderately effective, or are only effective for specific types of diseases. Pharmacological treatments can produce undesirable side effects and may not provide immediate relief.